Objective: Mean uterine artery pulsatility index (meanUAPI) is commonly measured at 11–13<sup>+6</sup> weeks to predict adverse pregnancy outcomes including hypertensive disorders and small-for-gestational age. The aims of this study were to establish a population-specific reference range for meanUAPI at <11 weeks, to determine if an abnormal meanUAPI at <11 weeks was associated with adverse pregnancy outcome, and to assess changes in meanUAPI between <11 weeks and 11–13<sup>+6</sup> weeks. Methods: A prospective cohort was examined at <11 weeks and at 11–13<sup>+6</sup> weeks to develop reference ranges for meanUAPI. Based on these regression models, meanUAPI Z-scores were compared between outcome groups using a two-sample t test. Longitudinal changes in the meanUAPI between <11 and 11–13<sup>+6</sup> weeks were assessed by two-way mixed ANOVA. Results: Prior to 11 weeks, there was no significant difference in meanUAPI between normal (n = 622) and adverse (n = 80) outcomes (mean [95% CI]: 2.62 [2.57–2.67] and 2.67 [2.50–2.84], respectively; p = 0.807). At 11–13<sup>+6</sup> weeks, meanUAPI was significantly higher in the adverse (n = 66) compared with the normal (n = 535) outcome group (mean [95% CI]: 1.87 [1.70–2.03] and 1.67 [1.63–1.72], respectively; p = 0.040). There was a statistically significant decrease (p < 0.0001) in meanUAPI between the two time points. Conclusion: MeanUAPI measured at <11 weeks’ gestation does not appear to be a useful marker for the prediction of placental-related adverse pregnancy outcomes, supporting an argument for the prediction of risk at 11–13<sup>+6</sup> weeks’ gestation.